1. Field of the Invention
The present invention relates to a liquid crystal display device for use in office automation (OA) equipment (e.g., word processors and personal computers), portable information equipment (e.g., electronic books), video cassette recorders (VCRs) incorporating a liquid crystal monitor, and the like.
2. Description of the Related Art
Recently, liquid crystal display devices have been widely used in OA equipment (e.g., word processors and personal computers), portable information equipment (e.g., electronic books), video cassette recorders (VCRs) incorporating a liquid crystal monitor and the like, utilizing the features of a thin display thickness and low power consumption.
Such liquid crystal display devices include a transmission-type liquid crystal display device using a thin, transparent, electrically conductive film such as ITO (Indium Tin Oxide) as pixel electrodes, and a reflection-type liquid crystal display device using reflective electrodes of, for example, a metal as pixel electrodes.
Unlike CRTs (cathode ray tubes) and EL (electroluminescence), liquid crystal display devices are not self-light-emitting display devices. Therefore, in the case of the transmission-type liquid crystal display device, an illumination device such as a fluorescent tube, which is a so-called backlight, is placed behind the liquid crystal display device, whereby a display is provided using incident light of the backlight. On the other hand, in the case of the reflection-type liquid crystal display device, a display is provided by reflecting incident light from the outside by the reflective electrodes.
Since the transmission-type liquid crystal display device uses the backlight to provide a display, the transmission-type liquid crystal display device has an advantage of providing a bright, high-contrast display without being significantly affected by the brightness around the liquid crystal display device. However, the backlight consumes about 50% or more of the overall power consumption of the liquid crystal display device, whereby power consumption is disadvantageously increased.
On the other hand, since the reflection-type liquid crystal display device does not use such a backlight, the reflection-type liquid crystal display device has an advantage of significantly reducing power consumption. However, brightness and contrast of the display are effected by environmental factors such as brightness around the liquid crystal display device and/or the conditions under which the liquid crystal display device is used.
In the case of the reflection-type liquid crystal display device, visual recognition of the display is affected by environmental factors such as brightness around the liquid crystal display device, and is extremely deteriorated particularly when ambient light is dark. On the other hand, in the case of the transmission-type liquid crystal display device, visual recognition of the display is reduced when ambient light is extremely bright such as in good weather.
As means for solving such problems, liquid crystal display devices having functions of both reflection- and transmission-type liquid crystal display devices (hereinafter, referred to as xe2x80x9ctransmission/reflection-type liquid crystal display devicesxe2x80x9d) are disclosed in copending U.S. application Ser. No. 09/122,756 filed on Jul. 27, 1998; U.S. application Ser. No. 09/220,792 filed on Dec. 28, 1998, which is a continuation-in-part application of U.S. application Ser. No. 09/122,756; and U.S. application Ser. No. 09/523,658 filed on Mar. 10, 2000, which is a continuation-in-part application of U.S. application Ser. No. 09/122,756. These U.S. applications are incorporated herein by reference.
In the transmission/reflection-type liquid crystal display devices proposed by the above-mentioned U.S. applications, each pixel region includes a reflective electrode region for reflecting ambient light and a transmissive electrode region for transmitting light from a backlight, the transmissive electrode region being formed from a film having a relatively high light-reflectance. As a result, the transmission/reflection-type liquid crystal display device (i) serves, in a pitch-dark environment, as a transmission-type liquid crystal display device which provides a display by using light from the backlight transmitted through the transmissive electrode regions, (ii) serves, in a dark environment, as a transmission/reflection-type liquid crystal display device which provides a display by using both light from the backlight transmitted through the transmissive electrode regions and ambient light reflected by the reflective electrode regions, and (iii) serves, in a bright environment, as a reflection-type liquid crystal display device which provides a display by using light reflected from the reflective electrode regions.
Hereinafter, the terms xe2x80x9creflective electrode regionxe2x80x9d, xe2x80x9ctransmissive electrode regionxe2x80x9d, xe2x80x9creflective regionxe2x80x9d and xe2x80x9ctransmissive regionxe2x80x9d as used herein will be defined.
A display device which provides a display in a reflection mode by using ambient light has reflective electrode regions for reflecting ambient light transmitted through a liquid crystal layer, the reflective electrode regions being provided on one of a pair of substrates. The reflective electrode region may be formed from a reflective electrode, or may be formed from a combination of a transparent electrode and a reflective layer (reflective plate). In other words, an electrode for applying a voltage to the liquid crystal layer may be formed from the transparent electrode, and the reflective layer for reflecting incident light does not have to function as an electrode.
In the display device according to the present invention, a region for providing a display in a transmission mode is referred to as a transmissive region, whereas a region for providing a display in a reflection mode is referred to as a reflective region. The transmissive region includes a transmissive electrode region and a liquid crystal region defined by the transmissive electrode region, and the reflective region includes a reflective electrode region and a liquid crystal region defined by the reflective electrode region. Although a semi-transmission/reflection-type liquid crystal display device using a semi-transmissive/reflective film (i.e., a porous, reflective film) has reflective electrode regions and transmissive electrode regions, light passing through respective liquid crystal regions defined by the reflective electrode regions and transmissive electrode regions is mixed and overlaps each other. Therefore, a region for providing a display in a transmission mode (i.e., a transmissive region) and a region for providing a display in a reflection mode (i.e., a reflective region) cannot be defined independently. In other words, among the liquid crystal display devices each of which has a transmissive electrode regions and a reflective electrode region, a liquid crystal device in which a region for providing a display in a transmission mode and a region for providing a display in a reflection mode cannot be defined independently (that is, they substantially overlap each other) is referred to as a semi-transmission/reflection type liquid crystal display device.
The term xe2x80x9cpixel regionxe2x80x9d as used herein will now be described. The liquid crystal display device of the present invention includes a plurality of pixel regions for providing a display. A single pixel region indicates a portion (component) of the liquid crystal display device, which constitutes a pixel, i.e., a minimum unit of the display. Typically, in an active matrix-type liquid crystal display device having a counter electrode and a plurality of pixel electrodes which are switched by respective active devices (e.g., thin film transistors (TFTs)) formed in a matrix, each pixel region includes a respective pixel electrode, a counter electrode region facing the pixel electrode, and a liquid crystal region located therebetween. In a simple matrix-type (or passive matrix-type) liquid crystal display device having stripe-shaped electrodes (scanning electrodes and signal electrodes) which are formed on respective substrates so as to intersect each other with a liquid crystal layer interposed therebetween, a pixel region includes respective intersection regions of the corresponding scanning and signal electrodes and a liquid crystal region located at the intersection.
In a color display device, color filter regions are formed in a display region, and light passing through the color filter regions is controlled, thereby providing color display by an additive color mixing method. For example, in the case where the color filter regions correspond to the pixel regions, a single color picture element region is formed from three pixel regions: red pixel region (R-pixel region), green pixel region (G-pixel region) and blue pixel region (B-pixel region). The color filter regions are regions which are provided in a color filter layer, and each of them indicates, for example, a red filter region (R-filter region), a green filter region (G-filter region) or a blue filter region (B-filter region). A color filter region is a portion of a respective color layer (i.e., red layer (R-layer), green layer (G-layer) or blue layer (B-layer)). A layer including a plurality of color layers is herein referred to as a color filter layer. In the case where the plurality of color layers are arranged in stripes, the color filter layer includes a plurality of R-layers, G-layers and B-layers which are arranged in a cyclic manner (i.e., RGBRGB . . . ). The color filter layer may include a light-shielding layer (black mask) provided between the color layers or between the color filter regions. A region having no color layer is herein referred to as a transmissive non-color filter region. In the present invention, the color filter layer includes color filter regions and transmissive non-color filter regions.
It should be noted that the term xe2x80x9cretardationxe2x80x9d as used herein indicates retardation with respect to light which is incident perpendicularly to a liquid crystal layer or phase compensation element (e.g., quarter-wave plate or half-wave plate) unless otherwise specified.
The above-mentioned transmission/reflection-type liquid crystal display device can always provide excellent visual recognition of display regardless of the brightness of ambient light. However, in the case where a conventional color filter is used for color display, optimum color display cannot be obtained both in a transmission mode and reflection mode. For example, the brightness of outside light is changed, visual recognition of the color display deteriorates.
FIG. 30 is a plan view showing the case where a normal color filter layer 24 as conventionally used is provided in the above-mentioned transmission/reflection-type liquid crystal display device. As shown in FIG. 30, the color filter layer 24 includes color filter regions 24A, 24B and 24C. Each of the color filter regions 24A, 24B and 24C is a part of a respective stripe-shaped color layer (i.e., R-layer, G-layer or B-layer), and is formed so as to entirely cover a respective pixel region having a reflective electrode region (R region) 3 and a transmissive electrode region (T region) 8.
In the case where such a conventional color filter layer 24 is applied to the above-mentioned transmission/reflection-type liquid crystal display device as shown in FIG. 30, light from the backlight is transmitted through a color filter layer in a transmissive region only once, whereas ambient light is transmitted through a color filter layer in a reflective region twice due to the reflection. Therefore, in the case where the same color filter is used both in the transmissive region and reflective region, display in the reflective region becomes dark. For example, a transmittance of a color filter for use in a normal transmission-type liquid crystal display device is about 30% after human eye""s color sensitivity collection, while being about 16% when this color filter is used in a reflection-type liquid crystal display device.
Japanese Laid-Open Publication No. 8-286178 discloses a liquid crystal display device which realizes bright, high chromaticity-property color display, wherein a color filter has an island-shaped color portion in each pixel, and an opening (i.e., a region having no color portion) is provided around each color portion. However, Japanese Laid-Open Publication No. 8-286178 merely discloses the structure of the color filter layer for use in a transmission- or reflection-type liquid crystal display device, and fails to disclose an optimal structure of a color filter layer for use in a transmission/refection-type liquid crystal display device including, in every pixel region, both a reflective electrode region for reflecting ambient light and a transmissive electrode region for transmitting light from the backlight. In other words, Japanese Laid-Open Publication No. 8-286178 fails to disclose features and arrangement of color filter region (i.e., color portion) and transmissive non-color filter region (i.e., opening). When the technique of forming a color filter as disclosed in Japanese Laid-Open Publication No. 8-286178 is applied to such a transmission/reflection-type liquid crystal display device, only a light-colored, low chromaticity-property display can be obtained. Therefore, it is very difficult to realize a color filter capable of providing a bright, high chromaticity-property color display both in the transmissive and reflective regions. Moreover, in the case where a substrate having a color filter layer and a substrate having electrodes used for display are laminated to each other so as to be shifted from each other, that is, in the case where the substrates are mis-aligned with respect to each other, the transmissive non-color filter regions protrude into the transmissive regions, thereby reducing chromaticity property.
According to one aspect of the present invention, a color filter layer includes a first region and a second region, wherein the number of times that light used for display is transmitted through the color filter layer is different between the first region and the second region.
In one embodiment of the present invention, the first and second regions of the color filter layer are formed so that a difference in a chromaticity property between the light used for display in the first region and the light used for display in the second region is small.
According to another aspect of the present invention, a display device includes: a first substrate having a display region, the display region including at least one reflective region in which light is reflected by a reflection means and at least one transmissive region through which light is transmitted; and a color filter layer including at least one first region and at least one second region, wherein the number of times that light used for display is transmitted through the color filter layer is different between the at least one first region and the at least one second region.
In one embodiment of the present invention, the color filter layer is formed so that a difference in a chromaticity property between the light used for display in the at least one first region and the light used for display in the at least one second region is small.
In another embodiment of the present invention, light used for display in the at least one first region is light which has been reflected by the reflection means of the at least one reflective region; and light used for display in the at least one second region is light which has been transmitted through the at least one transmissive region.
In still another embodiment of the present invention, the at least one reflective region includes a liquid crystal layer and a reflective electrode region which performs as the reflection means and which provides a voltage to the liquid crystal layer of the at least one reflective region; and the at least one transmissive region includes a liquid crystal layer and a transmissive electrode region which provides a voltage to the liquid crystal layer of the at least one transmissive region.
In still another embodiment of the present invention, the display device further includes a second substrate which faces the first substrate.
In still another embodiment of the present invention, the at least one first region and the at least one second region each include a color filter region, the color filter region giving a color to light which passes through the color filter region.
In still another embodiment of the present invention, the at least one first region includes a transmissive non-color filter region.
In still another embodiment of the present invention, in the at least one first region, the transmissive non-color filter region is provided over or under the color filter region in the color filter layer.
In still another embodiment of the present invention, the color filter layer is provided on the first substrate.
In still another embodiment of the present invention, the transmissive non-color filter region is positioned between the first substrate and the color filter layer.
In still another embodiment of the present invention, the display device further includes a second substrate on which the color filter layer is provided.
In still another embodiment of the present invention, in the at least one first region, the transmissive non-color filter region is positioned between the second substrate and the color filter region.
In still another embodiment of the present invention, a thickness of the color filter region in at least a portion of the at least one first region is different from a thickness of the color filter region in the at least one second region which produces a same color type as that produced in the at least one first region.
In still another embodiment of the present invention, a material used for the color filter region in the at least one first region is the same as that used for the color filter region in the at least one second region which produces a same color type as that produced in the at least one first region.
In still another embodiment of the present invention, a thickness of the color filter region in at least a portion of the at least one first region is different from that of the color filter region in the at least one second region which produces a same color type as that produced in the at least one first region.
In still another embodiment of the present invention, a material used for the color filter region in the at least one first region is the same as that used for the color filter region in the at least one second region which produces a same color type as that produced in the at least one first region.
In still another embodiment of the present invention, the color filter layer includes a plurality of first regions; and each of the plurality of first regions has the same ratio of an area ratio of the color filter region to the transmissive non-color filter region.
In still another embodiment of the present invention, a transmissivity at least a portion of the at least one first region for a wavelength in a certain wavelength range is less than a transmissivity for a wavelength in the certain wavelength range of the at least one second region which produces a same color type as that produced in the at least one first region.
In still another embodiment of the present invention, a material used for the color filter region in the at least one first region is different from that used for the color filter region in the at least one second region which produces a same color type as that produced in the first region.
According to one aspect of the present invention, a liquid crystal display device includes: a first substrate; a second substrate; a liquid crystal layer interposed between the first and second substrates; a plurality of pixel regions for providing a display; and a reflective region for providing a display by using reflected light, the reflective region being provided in each of the plurality of pixel regions, wherein the first substrate includes a reflective electrode region in the reflective region, the second substrate includes a color filter layer, the color filter layer having a color filter region and a non-color filter region in the reflective electrode region, and the color filter region and the non-color filter region are located such that an overlapping area of the reflective electrode region and the non-color filter region is not changed even when the first and second substrates are mis-aligned with respect to each other.
In one example, the color filter layer includes a light-shielding region between the color filter region and the non-color filter region.
According to another aspect of the present invention, a liquid crystal display device includes: a first substrate; a second substrate; a liquid crystal layer interposed between the first and second substrates; a plurality of pixel regions for providing a display; and a reflective region for providing a display by using reflected light and a transmissive region for providing a display by using transmitted light, the reflective region and the transmissive region being provided in each of the plurality of pixel regions, wherein the first substrate includes a reflective electrode region in the reflective region and a transmissive electrode region in the transmissive region, the second substrate includes a color filter layer, the color filter layer having a color filter region and a non-color filter region in the reflective electrode, and the color filter region and the non-color filter region are located such that an overlapping area of the reflective electrode region and the non-color filter region is not changed even when the first and second substrates are mis-aligned with respect to each other.
In one example, the transmissive region includes the color filter region located on the second substrate.
On one example, the color filter layer includes a light-shielding region between the color filter region and the non-color filter region.
In one example, each of the plurality of pixel electrodes has the same ratio of an area of the color filter region to an area of the non-color filter layer in the reflective region.
In one example, a ratio of the area of the non-color filter region to an area of the reflective region is in a range of about 0.05 to about 0.2.
In one example, the color filter layer includes one of a blue filter region, a red filter region and a green filter region in each of the plurality of pixel regions, wherein in a pixel region having the blue filter region, a ratio of an area of the non-color filter region to an area of the reflective region is in a range of about 0.05 to about 0.2; in a pixel region having the red filter region, a ratio of an area of the non-color filter region to an area of the reflective region is in a range of about 0.05 to about 0.38; and in a pixel region having the green filter region, a ratio of an area of the non-color filter region to an area of the reflective region is in a range of about 0.05 to about 0.5.
In one example, the liquid crystal layer includes a liquid crystal material exhibiting negative dielectric anisotropy, and a quarter-wave plate and a polarizing plate are provided on each of the first and second substrates with the first and second substrates interposed therebetween.
In one example, the reflective electrode region has a light-diffusing structure having an uneven surface.
In one example, a planarizing layer having a light transmitting property is formed in the non-color filter region.
In one example, the first substrate further includes a switching device provided in each of the plurality of pixel regions, the reflective electrode region includes an insulation layer and a reflective electrode formed on the insulation layer, the reflective electrode and the switching device being electrically connected to each other through a contact hole formed in the insulation layer, and the second substrate has the color filter region at a portion facing the contact hole.
Hereinafter, functions of the present invention will be described briefly.
A liquid crystal display device of the present invention includes a pair of substrates which are laminated to each other with a liquid crystal layer interposed therebetween, and also includes reflective regions for providing a display by using reflected light, wherein reflective electrode regions are formed on one of the substrates, and a color filter layer including color filter regions is formed on the other substrate. A color filter region(s) and a non-color filter region(s) are formed on the respective reflective region of the color filter substrate. This color filter layer is formed such that the area of the non-color filter region(s) in each reflective region is not changed even when the pair of substrates (i.e., the reflective electrode regions and the color filter regions) are not accurately laminated to each other (i.e., the pair of substrates are mis-aligned with respect to each other). Therefore, variation in optical characteristics of the liquid crystal device (e.g., brightness and chromaticity property) can be minimized even when a finished pattern of the edge portion of the color filter region is varied upon producing the color filter layer, as well as even when the substrates are mis-aligned upon producing the liquid crystal panel.
Moreover, a black mask (light-shielding region) having a line width larger than the variation in a finished pattern of the edge portion of the color filter region is formed at least on the boundary between the color filter region and non-color filter region. As a result, variation in display characteristics such as chromaticity property and contrast can be minimized even when the finished pattern of the edge portion of the color filter region is varied.
According to the present invention, a non-color filter region is provided in the respective reflective regions of the other substrate in a transmission/reflection-type liquid crystal display device, whereby white display can be provided as well as brightness of the display can be improved without increasing the number of steps in the production process as compared to the case where the color filter layer for use in the transmission-type liquid crystal display device is used. This is because a thickness of the color layers of the color filter layer need not be adjusted separately in the transmissive electrode region and reflective electrode region. In the conventional examples, brightness and chromaticity property have been optimized for each of the color layers. Therefore, it has been difficult to select a type of pigment and to adjust a concentration of the pigment dispersed in a resin. However, according to the present invention, brightness and chromaticity property can be optimized only by the design of a mask pattern, whereby the production process is simplified as well as the restrictions in designing a liquid crystal display device can be reduced.
According to the present invention, light transmitted through the color filter regions having high chromaticity property is mixed with light transmitted through the non-color filter regions, whereby bright color display required for the reflection display can be realized.
Moreover, the color filter region(s) having high chromaticity property is/are provided in each transmissive region, whereby a display having high chromaticity property can be provided as in the case of the conventional transmission-type liquid crystal display devices.
In each pixel region, the ratio of the area of the color filter region(s) to the area of the non-color filter region(s) in the reflective region is the same. Therefore, different masks need not be used for producing different color layers (i.e., R, G and B layers) of the color filter layer by using an exposure process. In other words, each of the R, G and B layers can be produced by merely shifting a single mask to a respective prescribed position and conducting the exposure process. As a result, the production process of the color filter layer can be simplified.
By setting the ratio of the area of the non-color filter region(s) to the area of the reflective region in the range of 0.05 to 0.2, color display having excellent brightness and chromaticity property can be realized. When the area of each non-color filer region is uniformly increased in order to increase the brightness, the brightness is improved, whereas the chromaticity property is reduced, and finally, display cannot be distinguished from white display. In other words, when the ratio of the area of the non-color filter region(s) to the area of the reflective region is set to less than about 0.05, sufficient brightness cannot be obtained in reflection display, resulting in a defective display. On the other hand, when the ratio of the area of the non-color filter region(s) to the area of the reflective region is set to more than about 0.2, the chromaticity property is reduced, resulting in a light-colored display which cannot be distinguished from white display (see, for example, FIGS. 25 and 26).
Moreover, the color filter layer includes one of R, G, B filter regions in each pixel region. The ratio of the area of the non-color filter region(s) to the area of the reflective region in a pixel region having a B filter region is set in the range of about 0.05 to about 0.2. The ratio of the area of the non-color filter region(s) to the area of the reflective region in a pixel region having a R filter region is set in the range of about 0.05 to about 0.38. The ratio of the area of the non-color filter region(s) to the area of the reflective region in a pixel region having a G filter region is set in the range of about 0.05 to about 0.5. Thus, brightness and chromaticity property of each color can be retained, whereby a well-balanced color filter can be realized. Such setting of the ratios is done because respective optimal values of the brightness and chromaticity property are different for each color.
When the liquid crystal display device is in a normally black mode (e.g., the liquid crystal molecules are arranged in a crossed-Nicols arrangement in a vertical alignment mode), black display can be provided while a voltage is not applied. Therefore, leakage of light can be eliminated when the transmission/reflection-type liquid crystal display device of the present invention is used either as a reflection-type liquid crystal display device or as a transmission-type liquid crystal display device. As a result, reduction in contrast can be prevented.
Moreover, a liquid crystal material having negative dielectric anisotropy is used for the liquid crystal layer, and a quarter-wave plate and a polarizing plate are provided on each of the respective outer surfaces of the pair of substrates which face each other. Accordingly, a high-contrast display can be realized without changing the thickness of the liquid crystal layer in the transmissive region and reflective region.
Moreover, each reflective electrode region has an uneven surface so as to have a light-diffusing property. Therefore, a light-diffusing function can be obtained only by the reflective electrode regions, whereby a xe2x80x9cmirror effectxe2x80x9d in the reflective electrode regions can be prevented, as well as a paper-white display can be realized. The xe2x80x9cmirror effectxe2x80x9d herein means, for example, a phenomenon that a viewer""s face is reflected in a mirror.
Moreover, a planarizing film having a light-transmitting property is formed at least on each of the non-color filter regions, whereby the surface of the color filter substrate which faces the liquid crystal layer (i.e., the surface of the color filter substrate on which a counter electrode is formed) can be substantially planarlized. Accordingly, in each reflective region, a thickness of the portion of the liquid crystal layer which corresponds to the color filter region is made equal to a thickness of the portion of the liquid crystal layer which corresponds to the non-color filter region (i.e., a cell gap difference is eliminated). As a result, retardation in both portions of the liquid crystal layer is made equal to each other, whereby a uniform display can be realized from a dark state to a bright state. It should be noted that, when the planarizing film is formed from a colorless material, only the thickness of the liquid crystal layer can be adjusted by the planarizing film. Therefore, light is not absorbed in the color filer substrate, thereby preventing reduction in light utilization efficiency. Furthermore, designed color-reproduction of the color filter layer is not affected.
Moreover, the color filter layer is also formed on the region of the color filter substrate which corresponds to a contact hole for connecting a pixel electrode to a switching device, whereby the leakage of light within the reflective region, which results from the mismatch of the electro-optical characteristics due to the difference in retardation, is reduced. Accordingly, a defective display which occurs in the vicinity of the contact hole can be eliminated, whereby a uniform display can be obtained in a dark state, gray state and bright state. Also, a higher contrast can be achieved.
Thus, the invention described herein makes possible the advantage of providing a display device which is capable of providing a high-quality color display regardless of the condition of ambient light.